Not really read up on it yet, but can you do serial over Bluetooth? Quick Google gave me this: https://raspberry-projects.com/pi/pi-operating-systems/raspbian/bluetooth/serial-over-bluetooth

There may even be an android app that could help. Suppose it depends on the scope of your project.

Funnily enough I may have to do something with this tech myself later in the year.

Rolling codes may protect you from a replay attack, but if the attacker is more sophisticated and has worked out the algorithm, then they can send the commands and effectively lock you out.

Is Bluetooth no good? Lots of protection baked in already.